Infrared-assisted freeze-drying (IRFD) of açai puree: Effects on the drying kinetics, microstructure and bioactive compounds

Comparison between near and far wavelength sections were evaluated in the infrared-assisted freeze-drying (IRFD) process of açai puree. Samples were dried using freeze drying (FD); near IRFD (NIRFD); far IRFD (FARFD); and infrared heating after 20% weight reduction, NIRFD20%WR and FARFD20%WR. IRFD significantly reduced the total drying time, with NIRFD and FARFD taking 49.42% and 33.40% less time than FD, respectively. The structure of powdered using IRFD was more open and with larger pores. FARFD20%WR had collapsed cells that compromised the functional properties of the powder (wettability, dispersibility). As for bioactive compounds, phenolic content was not affected by IRFD, ranging from 963.44 to 1025.60 mg/100 g. Antioxidant capacity increased (59.91 to 88.06%) when far infrared was used due to a Maillard reaction that generated antioxidant compounds and darker product. Content of anthocyanins reduced in samples dried by far infrared. Overall, NIRFD was more efficient, as it reduced total drying time without compromising product quality. The high-energy consumption of traditional freeze-drying limit the large-scale industrial production of freeze-dried açai puree. The infrared-assisted freeze-drying has been contributions on reducing drying energy consumption with time saving varying from 24.73 to 49.42% compared to the conventional freeze-drying treatment, maintaining the color, appearance and nutritional quality of the açai puree. Besides that, this study outstands that near wavelength lamps are more suitable for food drying by IRFD.